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Stack Exchange is a fast-growing network of Question and Answer sites on diverse topics from software development to cooking to photography and gaming. It is an expert knowledge exchange: a place where physics researchers can ask each other about quantum entanglement, computer programmers can ask about JavaScript date formats, and photographers can share knowledge about taking great pictures in the snow.

After someone asks a question, members of the community propose answers. Others vote on those answers. Very quickly, the answers with the most votes rise to the top. You don’t have to read through a lot of discussion to find the best answer.

Like topics on Wikipedia, questions and answers on Stack Exchange can be edited. If someone writes the beginning of a great answer, someone else can embellish it and make it even better.

The site is free and open to everyone. You don’t have to register, but if you do, you collect reputation points when people vote up your answers, which will appear next to your name.

What’s special about Stack Exchange?

You wouldn’t shout out a calculus question in a football stadium, right? You’d go to the math department of a university. That’s why instead of allowing questions on any topic, we have brought together separate communities of experts on very specific topics.

We don’t open a site until we’re sure there’s a critical mass of experts ready to participate. If you can’t find a Stack Exchange site on your subject of expertise, we have a place called Area 51 where you can propose one.

All questions on Stack Exchange are expected to be objective and have concrete answers; we’re not a place for conversation, opinions, or socializing. We also expect questions to represent real problems, not just imponderables, hypotheticals, or requests for opinions.

Stack Exchange’s focus on professional communities and this “Just the facts, Ma’am” ethos results in over 90% of questions getting great answers, often stunningly quickly.

What’s the story behind Stack Exchange?

In 2008, Jeff Atwood and Joel Spolsky created a site called Stack Overflow and brought together millions of computer programmers from around the world to help each other with detailed technical questions. That site was a phenomenal success, so, after securing a $6 million investment from Union Square Ventures, they created the Stack Exchange Network and started launching new sites in August of 2010. There are now 69 separate sites and over 19 million unique visitors (as of January, 2011) —and growing!